docs: add environment setup instructions

- Add .env.example file with template for secure configuration
- Update Quick Start section with detailed environment setup
- Provide both .env file and docker-compose variable methods
- Add security notes and password generation commands
- Document default database credentials with security warning
- Include instructions for generating secure JWT secrets and passwords

.env.example

@@ -0,0 +1,8 @@
+# Environment Variables
+# Copy this file to .env and update the values
+
+# JWT Secret for authentication (generate a secure random string)
+JWT_SECRET=your-secure-jwt-secret-key-here
+
+# PostgreSQL database password
+DBPASS=your-secure-database-password-here

README.md

@@ -32,16 +32,68 @@ A self-hosted ebook management system built with Go, PostgreSQL, HTMX, and Tailw
 
 - Docker and Docker Compose
 
+### Environment Setup
+
+**Option 1: Create .env file**
+```bash
+# Copy the example environment file
+cp .env.example .env
+
+# Edit with your secure values
+nano .env  # or your preferred editor
+```
+
+**Required Environment Variables:**
+- `JWT_SECRET` - Secure random string for JWT authentication
+- `DBPASS` - PostgreSQL database password
+
+### Generating Secure Values
+
+**Generate JWT Secret:**
+```bash
+# Generate 64-byte secure random string
+JWT_SECRET=$(openssl rand -base64 64)
+```
+
+**Generate Database Password:**
+```bash
+# Generate 32-character secure password
+DBPASS=$(openssl rand -base64 32 | tr -d '=' '/+' | cut -c1-32)
+```
+
+**Add to .env:**
+```bash
+echo "JWT_SECRET=$JWT_SECRET" >> .env
+echo "DBPASS=$DBPASS" >> .env
+```
+
 ### Running the Application
 
+**Option 1: Using .env file**
 1. Clone the repository
-2. Run the application:
+2. Set up environment:
-
+   ```bash
+   cp .env.example .env
+   # Edit .env with your secure values
+   ```
+3. Run the application:
    ```bash
    docker-compose up --build
    ```
+4. Access the application at http://localhost:8765
 
-3. Access the application at http://localhost:8765
+**Option 2: Using docker-compose variables**
+1. Clone the repository
+2. Set environment variables directly:
+   ```bash
+   export JWT_SECRET="your-secure-jwt-secret-key-here"
+   export DBPASS="your-secure-database-password-here"
+   ```
+3. Run the application:
+   ```bash
+   docker-compose up --build
+   ```
+4. Access the application at http://localhost:8765
 
 ### Database
 
@@ -50,6 +102,8 @@ PostgreSQL runs on port 5432 with default credentials:
 - User: postgres
 - Password: password
 
+**⚠️ Security Note**: Change the default password in production environments! Use the `DBPASS` environment variable to set a secure password.
+
 ## Development
 
 ### Development